Ultrasound Imaging

ABSTRACT

An ultrasound imaging system ( 102 ) includes a transducer array ( 108 ) with a two-dimensional non-rectangular array of rows ( 110 ) of elements, transmit circuitry ( 112 ) that actuates the elements to transmit an ultrasound signal into a field of view, receive circuitry ( 114 ) that receives echoes produced in response to an interaction between the ultrasound signal and a structure in the field of view, and a beamformer that processes the echoes, thereby generating one or more scan lines indicative of the field of view.

TECHNICAL FIELD

The following generally relates to imaging and finds particularapplication to ultrasound imaging and is described herein withparticular attention to an ultrasound imaging system.

BACKGROUND

Ultrasound (US) imaging has provided useful information about theinterior characteristics (e.g., organ tissue, material flow, etc.) of asubject under examination. A general US system includes a probe (with atransducer array) that interfaces with a console, which controls thetransducer elements of the transducer array to transmit an ultrasonicbeam and receive echoes produced in response thereto, which areprocessed to generate an image(s) of the interior characteristics. Thedetail and contrast resolutions of the imaging system depend at least onthe shape of the ultrasonic beam, which has dimensions both in theimaging plane (azimuth or lateral) and across the imaging plane(elevation).

A one dimensional (1D) transducer array includes a single row oftransducer elements arranged along the lateral direction, and the beamis electronically controlled in the lateral direction. The width of thetransducer elements is on the order of a wave length. By controlling thedelays and weight coefficients in the beamforming, the focus can becontrollably moved along a line. In the elevation direction, the heighthas been several millimeters (e.g., 4 to 20 mm). The focusing in theelevation plane is achieved with acoustic lenses, and the focus isgenerally fixed. The beam is narrowest at the elevation focus anddiverges beyond it. Close to the transducer, the beam is as wide as thetransducer array, and away from the elevation focus, the beam becomeseven wider.

A 1.5D array has several rows of elements. The effective size of theelements in elevation direction is usually much larger than the width.The outer rows are electrically connected to the middle row. A switchalternately couples outer rows to the middle row, depending on thedistance from the transducer surface, creating large elements at largedepths. Such arrays have had acoustic lenses that focus the beam inelevation direction. Unfortunately, there is no control over the delaysin the elevation plane so there is a trade-off between beam size and theuniformity in the elevation plane. 1.75D array is similar to a 1.5Darray, but each element is connected to a channel. This allowselectronic focusing in the elevation direction. Unfortunately, thenumber of channels increases, e.g., from N to 2N, relative to a 1.5Darray with N channels.

A synthetic transmit aperture has been used to increase image quality.In one instance, this includes sequentially actuating two or more of thetransduce elements, invoking transmissions of two or more ultrasoundsignals, where the echoes generated in response to each transmissionhave different phase and/or amplitude information. For eachtransmission, all of the transducer elements receive echoes, which arebeamformed to generate a lower resolution image for each set of receivedechoes. The lower resolution images are accumulated and/or otherwisecombined to generate a higher resolution image. Generally, a highernumber of transmissions results in higher image quality, but lower framerate. Therefore, unfortunately, there is a trade-off between imagequality and frame rate.

Coded excitation has been used to increase the signal-to-noise ratio.Examples of spread codes include, but are not limited to, Barker codes,Golay codes, and frequency modulated (FM) pulses. FM modulated pulsestend to be robust to frequency-dependent attenuation and, in many cases,gives the greatest increase in signal-to-noise ratio. An artifact ofusing FM pulses is the existence of range side-lobes (along the imagingdirection). These range side lobes are attenuated by tapering the risingand falling edges of the FM pulse. Typically, a Tukey windowing functionis used. This means that the transmitted pulses are both frequency andamplitude modulated. Sending such pulses usually requires either amulti-level linear sender (e.g. 12-bit) or bipolar square wave ([−1, 0,1]) operating at over 200 MHz clock frequency. Unfortunately, suchtransmitters tend to be costly.

Obese patients, generally, have a thicker layer of subcutaneous adiposetissue, relative to non-obese patients. The speed of sound in adiposetissue is on the order of 1450 m/s, while the speed of sound in organtissue tends to be higher. For example, the speed of sound in livertissue is on average about 1540 m/s. The sound waves refract duringtheir propagation (Snell's law). Delay calculations for beamforming havebeen based on straight lines of propagation. Unfortunately, this is notan accurate assumption in the case of layered media including adiposetissue and organ tissue.

SUMMARY

Aspects of the application address the above matters, and others.

In one aspect, an ultrasound imaging system includes a transducer arrayincluding a two-dimensional non-rectangular array of rows of elements,transmit circuitry that actuates the elements to transmit an ultrasoundsignal into a field of view, receive circuitry that receives echoesproduced in response to an interaction between the ultrasound signal anda structure in the field of view, and a beamformer that processes theechoes, thereby generating one or more scan lines indicative of thefield of view.

In another aspect, a method includes transmitting, with atwo-dimensional non-rectangular transducer array, an ultrasound signalinto a field of view, receiving, with the two-dimensionalnon-rectangular transducer array, echoes produced in response to aninteraction between the ultrasound signal and structure in the field ofview, and processing the received echoes, thereby generating scan linesindicative of the field of view.

In another aspect, a computer readable storage medium is encoded withcomputer executable instructions, which, when executed by a processor,causes the processor to: transmit, with a two-dimensionalnon-rectangular transducer array, an ultrasound signal into a field ofview, receive, with the two-dimensional non-rectangular transducerarray, echoes produced in response to an interaction between theultrasound signal and structure in the field of view, process thereceived echoes, thereby generating scan lines indicative of the fieldof view.

Those skilled in the art will recognize still other aspects of thepresent application upon reading and understanding the attacheddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

The application is illustrated by way of example and not limitation inthe figures of the accompanying drawings, in which like referencesindicate similar elements and in which:

FIG. 1 illustrates an example ultrasound imaging system;

FIG. 2 illustrates an example of the transducer array with a physicalnon-rectangular array;

FIG. 3 illustrates the footprint of the transducer array of FIG. 2;

FIG. 4 illustrates a side view of the transducer array of FIG. 2 inconnection with a single focusing lens;

FIG. 5 illustrates a side view of the transducer array of FIG. 2 inconnection with multiple focusing lenses;

FIG. 6 illustrates an example of the transducer array with a virtualnon-rectangular array;

FIG. 7 illustrates an example multi-level transmitter;

FIG. 8 illustrates an example diagram; and

FIG. 9 illustrates an example method.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates an example imaging system 102, such asultrasonic (US) imaging system. The imaging system 102 includes anultrasound transducer probe 104 and a console 106. The ultrasoundtransducer probe 104 interfaces with the console 106 through a suitableinterface.

The ultrasound transducer probe 104 includes a two-dimensional (2D)transducer array 108. Generally, the transducer array 108 converts anelectrical signal to an ultrasound pressured field and vice versa. Morespecifically, the elements of the rows are configured to transmitultrasound signals in a field of view and receive echo signals generatedin response to an interaction of the transmit ultrasound signals withstructure in the field of view. The transducer array 108 can be linear,curved, and/or otherwise shaped, fully populated, sparse and/or acombination thereof, etc.

The illustrated transducer array 108 includes N rows 110 (where N is aninteger equal to or greater than three, such as 3, 5, 9, 11, etc.),including a center row 110 _(C) and pairs of outer rows 110 _(1a) and110 _(1b) (collectively referred to herein as first pair of outer rows110 ₁), . . . , 110 _(Ma) and 110 _(Mb) (collectively referred to hereinas Mth pair of outer rows 110 _(M)), where C, a, b, and M are integers.The center row 110 _(C) includes I elements, 110 _(C1), 110 _(C2), . . ., 110 _(CI), where I is an integer. The first pair of outer rows 110 ₁includes J elements, 110 ₁₁, 110 ₁₂, . . . , 110 ₁₁, . . . , and thepairs of outer rows 110 _(M) includes K elements, 110 _(M1), 110 _(M2),. . . , 110 _(MK), where J and K are integers

Each of the rows 110 is arranged along a lateral direction 111 of thetransducer array 108, with the rows 110 arranged generally parallel toeach other along an elevation direction 113 of the transducer array 108.The rows 110 _(1a) and 110 _(1b) of the first pair of rows 110 ₁ arearranged on opposite sides of the center row 110 _(C) A next pair ofrows 110 (not visible) is arranged on opposite sides of the first pairof rows 110 ₁, . . . , and the rows 110 _(Ma) and 110 _(Mb) of the Mthpair of rows 110 _(M) are arranged on opposite sides of an (M−1)th pairof row 110 (not visible). Note that the illustrated geometry (e.g.,width and height) is for explanatory purposes and does not correspond tothe actual geometry.

As described in greater detail below, in one instance, the elements ofthe transducer array 108, in aggregate, have a non-rectangular shape(e.g., a generally elliptical shape) in that the center row 110 _(C)includes more elements than the outer rows 110 _(1a), 110 _(1b), 110_(Ma) and 110 _(Mb). In one instance, this includes a transducer array108 with a center row 110 _(C) that is populated with more elements thanthe rows 110 _(1a), 110 _(1b), 110 _(Ma) and 110 _(Mb). In anotherinstance, the elliptical shape corresponds to a number of activeelements where more elements along the center row 110 _(C) are activerelative to the outer rows 110 _(1a), 110 _(1b), . . . , 110 _(Ma) and110 _(Mb).

The console 106 includes transmit circuitry 112 that selectivelyactuates or excites one or more of the transducer elements of thetransducer array 108. More particularly, the transmit circuitry 112generates a set of pulses (or a pulsed signal) that are conveyed to thetransducer array 108. The set of pulses actuates a set of the transducerelements of the transducer array 108, causing the elements thereof totransmit ultrasound signals into an examination or scan field of view.As described in greater detail below, in one instance, the transmitcircuitry 108 is configured for coded excitations, which may facilitateimproving the signal to noise ratio, relative to a configuration withoutcoded excitations.

Receive circuitry 114 receives a set of echoes (or echo signals)generated in response to the transmitted ultrasound signals. The echoes,generally, are a result of the interaction between the emittedultrasound signals and the object (e.g., flowing blood cells, organcells, etc.) in the scan field of view. The receive circuit 116 may beconfigured for spatial compounding, filtering (e.g., FIR and/or IIR),and/or other echo processing.

A beamformer 116 processes the received echoes, e.g., by applying timedelays and weights to the echoes and summing the resulting echoes. Asdescribed in greater detail below, in one instance the beamformer 116utilizes a layered model to solve Snell's law and correct forpropagation path and/or propagation delays. As such, the system 102 mayprovide for better focusing, which results in higher penetration depth,higher contrast resolution and higher detail resolution, with a fastcalculation time.

An optional synthetic aperture processor 118 is configured to generate asynthetic transmit and/or receive aperture. For synthetic transmitreceive aperture, the synthetic aperture processor 118 accumulates lowerresolution beamformed echoes with different phase and/or amplitudeinformation, generating a higher resolution image. A synthetic transmitaperture can be used to increase image quality, e.g., signal-to-noiseratio, contrast and detail resolution, etc. Generally, the higher thenumber of transmissions, the higher the image quality and the lower theframe rate.

A scan converter 120 scan converts the data for display, e.g., byconverting the beamformed data to the coordinate system of a display ordisplay region used to visually present the resulting data. Theillustrated embodiment includes a display 122. However, the display 120may alternatively be a remote device interfaced with the console 106.Visual presentation may be through an interactive graphical userinterface (GUI), which allows the user to selectively rotate, scale,and/or manipulate the displayed data.

A user interface (UI) 124 include one or more input devices (e.g., abutton, a knob, a slider, etc.) and/or one or more output devices (e.g.,a display, etc.), which allows for interaction between with the system102. In one instance, the UI includes a software based and/or physicalcontrol that allows a user to select between higher image quality orhigh frame rate. The control activates/deactivates the syntheticaperture processor 118 and/or determines, based on a predeterminedprotocol, user input or otherwise, the number of transmissions and hencethe trade-off between image quality and frame rate.

The UI control gives the user control over the tradeoff between imagequality and frame rate, allowing the user to determine the focusingstrength of transmission. Generally, the minimum number of transmissionsis two. The shape of transmit beam determines the weighting coefficientsapplied onto the beams. In this example, the synthetic apertureprocessor 118 can employ a model 126 from a plurality of models, eachfor a different beam shape, from a bank of models, depending on the beamshape, to determine the weighting coefficients applied onto the beams.

A controller 128 controls the various components of the imaging system102. For example, such control may include actuating or excitingindividual or groups of transducer elements of the transducer array 108for an A-mode, B-mode, C-plane, and/or other data acquisition mode,steering and/or focusing the transmitted signal, etc., actuating thetransducer array 108 for steering and/or focusing the received echoes,etc.

The console 106 may include one or more processors that execute one ormore computer readable instructions encoded or embedded on computerreadable storage medium such as physical memory and other non-transitorymedium. Additional or alternatively, the instructions can be carried ina signal, carrier wave and other transitory or non-computer readablestorage medium. In one instance, executing the instructions, inconnection with the one or more processors, implements one or more ofthe beamformer 116, the synthetic aperture 118, and/or other componentsof the imaging system 102.

As briefly discussed above, the transducer array 108 includes amulti-rowed non-rectangular footprint. FIGS. 2, 3, 4 and 5 illustrate anon-limiting example of the transducer array 108. FIG. 2 shows a viewlooking into a transducing face 200 of the transducer array 108, FIG. 3illustrates a view looking into the transducer array 108, FIG. 4illustrates a side view of the transducer array 108 in connection with afocusing lens, and FIG. 5 illustrates a side view of the transducerarray 108 in connection with multiple focusing lenses.

For sake of brevity, the transducer array 108 is discussed in connectionwith a configuration in which N=3 for FIGS. 2 to 5. In otherembodiments, N>3. Initially referring to FIG. 2, again, the center row110 _(C) and the outer rows 110 _(1a) and 110 _(1b) are arrangedparallel with respect to each other along the elevation direction 113and each extends along the lateral direction 111, with the outer rowsouter rows 110 _(1a) and 110 _(1b) on opposite sides of the center row110 _(C). As shown, in this example, each of the rows 110 _(C), 110_(1a) and 110 _(1b) is approximately centered in the lateral direction111 about an imaginary central axis 202.

Widths (lateral direction) of the individual elements 204 (110 _(C1),110 _(C2), 110 _(C1) in FIG. 1), 206 (110 ₁₁, 110 ₁₂, . . . , 110 _(1J)in FIG. 1) and 208 (110 _(M1), 110 _(M2), . . . , 110 _(MK) in FIG. 1)in the rows 110 _(C), 110 _(1a) and 110 _(1b) and pitch (i.e., thedistance between centers of neighboring elements) are approximatelyequal. The widths and/or the pitch can be optimized based on thefrequency and beam steering. As such, a width of the active aperture inthe lateral direction 111 is given by the number of elements being used.

In this example, heights (elevation direction) of the individualelements in the rows 110 _(1a) and 110 _(1b) are equal and half of aheight of the individual elements in the row 110 _(C). With equal widthsand half the height, the area of a pair of elements of the rows 110_(1a) and 110 _(1b) is about equal to an area an element in the row 110_(C), and the electrical impedance is the same. In a variation, theheights of the elements 206 and 208 of the rows 110 _(1a) and 110 _(1b)are greater or less than half the height of the elements 204 in row 110_(C). The total height of all three rows combined is in a range of ten(10) to fifty (50) millimeters (mm).

Each of the individual elements 204 of the center row 110 _(C) is inelectrical communication with a different single channel. Eachcomplimentary pair of elements of the outer rows 110 _(1a), and 110_(1b) (e.g., 206 _(I) and 208 _(I)) is in electrical communication witha different single channel. Generally, a complimentary pair includes theelements along a same column as the particular center row element. Thus,there is a single channel for each element 204 and a single channel foreach complimentary pair of elements 206 and 208. Complimentary pairs ofelements 206 and 208 are symmetric relative to the beam, and are notsteered in the elevation direction 113.

In the illustrated example, J=½ I, where, from FIG. 1, J represents thenumber of elements 206 and 208 in the outer rows 110 _(1a) and 110th andI represents the number of elements 204 in the center row 110 _(C). Assuch, the transducer array 108 utilizes a total of 1.51 channels. Forinstance, where I=32, J=16, I=128, J=64, I=192, J=96, etc., thetransducer array 108 utilizes 48, 192, 288, etc. channels. As such, theillustrated transducer array 108 utilizes less channels than a 1.75Dtransducer array or other configuration in which J=I. In otherembodiments, I and J could be other values. In addition, J could beanother factor of I such as ¼, ¾, etc.

With the configuration of FIG. 2, the transducer array 108 has anon-rectangular shape, for example, a generally elliptical shape, asshown in this example. This configuration provides a uniformly narrowbeam in the elevation direction 113.

Turning to FIGS. 3 and 4, in one embodiment, a lens 402 such as anacoustic or other lens focuses the beam of the center row 110 _(C) at afocus distance 404. With respect to FIGS. 3 and 5, in anotherembodiment, the lens 402 focuses the beam of the middle row 110 _(C) atthe first focus distance 404, and lenses 502, such as Fresnel lenses,focus the beam from the outer rows 110 _(1a) and 110th at a second focusdistance of 504, which is further away from the transducer array 102than the first focus distance 404.

In one instance, the focus distances 404 and 504 are such that thefocusing number (f-number) is approximately the same. An example of asuitable f-number is in a range from five (5) to eight (8). It is to beappreciated that having approximately equal f-numbers facilitatesproducing a beam with a uniform shape. The delays applied to theelements in the outer rows 110 _(1a), and 110 _(1b) are taken intoconsideration the refraction of the acoustic energy inside of thelenses.

Although FIGS. 2, 3, 4 and 5 describe the transducer array 108 in aconnection with three rows, it is to be understood that the transducerarray 108 could be a phased array having more rows. By way of example,where there are 5 rows and 192 channels, the center row may have 128elements, whereas each of the outer rows would have 32 elements. Inanother example, the center row may have 96 elements, each of a firstset of outer rows would have 64 elements, and each of a second pair ofouter rows would have 32 elements. Other configurations are alsocontemplated herein.

In FIGS. 2-5, the transducer array 102 includes a multi-rowednon-rectangular footprint that provides a uniformly narrow beam in theelevation direction 113. One or more focusing lenses are utilized with asubset of the rows (FIG. 3) and, optionally, one or more Fresnel lensescan be utilized with other subsets of the rows (FIG. 4). Thisconfiguration allows for achieving elevation focusing with a lowernumber of channels relative to a multi-rowed rectangular footprintand/or creating a narrow beam in elevation direction both close to andfar from the transducer array 108.

FIG. 6 schematically illustrates another example of the transducer 108.However, in this example, the transducer array 108 includes amulti-rowed rectangular footprint (with the same number of elements ineach row). For explanatory purposes, the following will be described fora 192 element per row, 3 rows (576 elements in aggregate), 192 channeltransducer array 108. Furthermore, the widths of the elements 204, 206and 208 of the 3 rows are about equal and the height of the elements 206and 208 outer rows 110 _(1a) and 110 _(1b) is half of the height ofelements 204 of the center row 110 _(C).

In the illustration, the elements of the center row 110 _(C) are indexed1:192 and divided up into blocks of 32 elements, or blocks 602, 604,606, 608, 610 and 612. Reference numerals 614, 616, 618, 620, 622 and624 indicate the index range for each block. The elements in block 602,indexed 1:32, are respectively electrically connected, throughmultiplexers or the like, to channels 1:32, and so on for the remainingblocks, elements and channels. Reference numerals 626, 628, 630, 632,634 and 636 indicate the channel numbers.

The outer two rows 110 _(1a) and 110 _(1b) are also indexed 1:192 anddivided up into blocks of 32 elements, or blocks 638, 640, 642, 644, 646and 648. Likewise, reference numerals 614, 616, 618, 620, 622 and 624indicate the index range for each block. The elements in block 626,indexed 1:32, are respectively electrically connected, throughmultiplexers or the like, to channels 97:128, and so on for theremaining blocks, elements and channels. Reference numerals 650, 652,654, 656, 658 and 660 indicate the channel numbers.

This configuration allows for an active aperture of 192 elements (orother number of elements) along the center row 110 _(C), e.g., at smalldepths where the outer rows 110 _(1a) and 110 _(1b) are not needed, byelectrically connecting the elements 1:192 respectively to the channels1:192. This configuration also allows for an active aperture of lessthan 192 elements along the center row 110 _(C) and elements of bothouter rows 110 _(1a) and 110 _(1b), e.g., at larger depths.

For example, in one instance, elements 33:160 (616-622) of the centerrow 110 _(C) are electrically connected to channels 33:160 (628-634),and elements 1:32 (614) of both outer rows 110 _(1a) and 110 _(1b) areelectrically connected to channels 97:128 (650) and elements 161:192(624) of both outer rows 110 _(1a) and 110 _(1b) are electricallyconnected to channels 65:96 (660). The resulting “virtual” or activeaperture is non-rectangular (e.g., generally elliptical shaped) like thephysical arrangement of FIGS. 2-5. Likewise, this configuration providesa uniformly narrow beam in the elevation direction 113.

It is to be appreciated that this particular assignment of elements tochannels is not limiting. In addition, group sizes can be different, andindividual elements can be assigned on an individual and not groupbasis. Moreover, one or more of the rows may have more or less than 192elements, and there may be more or less than 192 channels.

Generally, this configuration introduces an offset in the channelconnections for the outer two rows 110 _(1a) and 110 _(1b). As a result,cross-like active apertures can be created anywhere on the transducersurface. Furthermore, very wide apertures can be created for scans closeto the transducer array 102. Moreover, this configuration allows forangular compounding.

As discussed above, the transmit circuitry 112 can be configured forcoded excitations. FIG. 7 schematically illustrates an example N-level(N≥5) transmitter 702 for coded excitations that is based on afirst-order sigma-delta modulator. As shown, the transmitter 702includes an analog to digital (A/D) converter 704 that quantizes aninput signal 706 summed with a negative of a previous output signal 708,producing a current output signal 710 having a value of −1, ½, 0, ½, or1, which drives the elements of the transducer array 108. The 5-levelquantized output signal over time is shown at 710.

The illustrated transmitter 702 is a 5-level transmitter. Such codingallows for creating FM pulses at less than 200 MHz, such as 150 MHz, 120MHz, 100 MHz and/or other frequency. In one instance, the performance ofsuch a system will be approximately identical to a 3-level, bipolarsquare wave transmitters operating at 200 MHz, when imagingobese-patients, but at a lower cost. For example, the transmitter 702can achieve a same quality of received signal as with lineartransmitters, but costs less.

The transmitter 702 can be implemented as part of the transmit circuitry112, the controller 126, another distinct component of the console 106,and/or other component of the console 106 and/or remote from the console106.

As discussed above, the beamformer 116 may utilize a layered model tosolve Snell's law and correct for the propagation path and propagationdelay. The following describes a non-limiting approach. An exampleparameterized delay function is illustrated in EQUATION 1:

$\begin{matrix}{{{T(\varphi)} = \sqrt{V_{0}^{2} + {\alpha \left( {1 - {\cos (\varphi)}} \right)} + {\beta \left( {1 - {\cos \left( {2\varphi} \right)}} \right)}}},} & {{EQUATION}\mspace{14mu} 1}\end{matrix}$

where

$V_{0} = {\sum\limits_{n = 1}^{N}{\frac{d_{n}}{v_{n}}.}}$

This function approximately matches and resembles the approximatesolution for linear transducers. Only cosine terms are included due tothe symmetry condition T(ϕ)=T (−ϕ).

The cos(ϕ) term to be found for each element position need not to beevaluated directly but can be found using the addition formulas fortrigonometric functions. For example, the cos(2ϕ) term can be foundusing the properties cos(2ϕ)=cos²(ϕ)−sin²(ϕ). α and β can be estimatedto minimize a difference between T_(Snell) and T(ϕ) over a range ofvalues for which EQUATION 1 is used to estimate the delays. Ideally thisminimization is done as a least square or a min-max optimization, butuseful results can also be obtained from just two known delays suitablydistributed over the entire range.

For example, α and β can be estimated for the range ϕ=0, . . . , ϕ₀ asfollows. 1) With reference to FIG. 8, find the sine to the angle, θ₀,that corresponds to the line from P1 to P0 based on EQUATION 2:

$\begin{matrix}{s_{1} = {{\sin \left( \theta_{0} \right)} = {\frac{r_{1}{\sin \left( \varphi_{0} \right)}}{\sqrt{r_{0}^{2} + r_{N}^{2} - {2r_{0}r_{N}{\cos \left( \varphi_{0} \right)}}}}.}}} & {{EQUATION}\mspace{14mu} 2}\end{matrix}$

2) Find the angle, ϕ₁, that corresponds to tracing from P1 with θ₀ asstarting angle, as shown in EQUATION 3:

ϕ₁=ϕ(s ₁).  EQUATION 3:

3) Calculate the delay, τ₁, as shown in EQUATION 4:

τ₁ =T _(SNELL)(S _(N) =s ₁).  EQUATION 4:

4) Repeat step 2) and 3) for another value s₂=⅔s₁, based on EQUATIONS 5and 6: EQUATION 5:

ϕ₂=ϕ(s ₂), and  EQUATION 5:

τ₂ =T _(SNELL)(S _(N) =s ₂).  EQUATION 6:

5) Inserting these values in EQUATION 2 and reorganizing rendersEQUATION 10:

$\begin{matrix}{\begin{bmatrix}{\tau_{1}^{2} - V_{0}^{2}} \\{\tau_{2}^{2} - V_{0}^{2}}\end{bmatrix} = {{\begin{bmatrix}\left( {1 - {\cos \; {e\left( \varphi_{1} \right)}}} \right) & \left( {1 - {\cos \; {e\left( {2\varphi_{1}} \right)}}} \right) \\\left( {1 - {\cos \; {e\left( \varphi_{2} \right)}}} \right) & \left( {1 - {\cos \; {e\left( {2\varphi_{2}} \right)}}} \right)\end{bmatrix}\begin{bmatrix}\alpha \\\beta\end{bmatrix}}.}} & {{EQUATION}\mspace{14mu} 10}\end{matrix}$

6) Calculate α and β as shown in EQUATIONS 11 and 12:

$\begin{matrix}{\mspace{79mu} {{\alpha = \frac{\begin{matrix}{{\left( {r_{1}^{2} - V_{0}^{2}} \right)\left( {1 - {\cos \left( {2\varphi_{2}} \right)}} \right)} -} \\{\left( {r_{2}^{2} - V_{0}^{2}} \right)\left( {1 - {\cos \left( {2\varphi_{1}} \right)}} \right)}\end{matrix}}{\begin{matrix}{{\left( {1 - {\cos \left( \varphi_{1} \right)}} \right)\left( {1 - {\cos \left( {2\varphi_{2}} \right)}} \right)} -} \\{\left( {1 - {\cos \left( \varphi_{2} \right)}} \right)\left( {1 - {\cos \left( {2\varphi_{1}} \right)}} \right)}\end{matrix}}},{and}}} & {{EQUATION}\mspace{14mu} 11} \\{\beta = {\frac{{\left( {1 - {\cos \left( \varphi_{1} \right)}} \right)\left( {\tau_{1}^{2} - V_{0}^{2}} \right)} - {\left( {1 - {\cos \left( \varphi_{2} \right)}} \right)\left( {\tau_{2}^{2} - V_{0}^{2}} \right)}}{\begin{matrix}{{\left( {1 - {\cos \left( \varphi_{1} \right)}} \right)\left( {1 - {\cos \left( {2\varphi_{2}} \right)}} \right)} -} \\{\left( {1 - {\cos \left( \varphi_{2} \right)}} \right)\left( {1 - {\cos \left( {2\varphi_{1}} \right)}} \right)}\end{matrix}}.}} & {{EQUATION}\mspace{14mu} 12}\end{matrix}$

This solution may provide for better focusing, which results in higherpenetration depth, higher contrast resolution and higher detailresolution. Furthermore, the solution has a fast calculation time, whichallows for better interactions with the user. The beamformer 116 can beconfigured to calculate beamforming delays based on predeterminedcriteria, for example, such as every time the setup of the ultrasoundsystem 100 changes the setup (e.g., line density, combination ofmodes—CFM/Doppler/THI/CHI, etc.).

FIG. 9 illustrates a method.

Note that the ordering of the following acts is for explanatory purposesand is not limiting. As such, one or more of the acts can be performedin a different order, including, but not limited to, concurrently.Furthermore, one or more of the acts may be omitted and/or one or moreother acts may be added.

At 902, an US probe transmits an ultrasound beam into a field of view.

The probe incudes a transducer array with a non-rectangular footprint(physical or virtual), e.g., as discussed in connection with FIGS. 2-6,and/or otherwise. Transmission can be achieved via a five or other levelFM transmitter and/or otherwise. Transmission can be tailored for imagequality or frame rate based on a user input, as discussed herein.

At 904, echoes generated in response thereto are received by the probe.

At 906, the echoes are beamformed.

Where the echoes are delayed, the delays can be determined as discussedherein, including using a layered model to correct for the propagationpath and propagation delay.

At 908, optional, a synthetic transmit aperture is created.

At 910, the scan converter converts the processed echoes to data fordisplay on a monitor.

At 912, the data is displayed.

The above may be implemented by way of computer readable instructions,encoded or embedded on computer readable storage medium, which, whenexecuted by a computer processor(s), cause the processor(s) to carry outthe described acts. Additionally or alternatively, at least one of thecomputer readable instructions is carried by a signal, carrier wave orother transitory medium.

The application has been described with reference to variousembodiments. Modifications and alterations will occur to others uponreading the application. It is intended that the invention be construedas including all such modifications and alterations, including insofaras they come within the scope of the appended claims and the equivalentsthereof.

What is claimed is:
 1. A method, comprising: transmitting, with atwo-dimensional non-rectangular transducer array, an ultrasound signalinto a field of view; receiving, with the two-dimensionalnon-rectangular transducer array, echoes produced in response to aninteraction between the ultrasound signal and structure in the field ofview; and processing the received echoes, thereby generating scan linesindicative of the field of view.
 2. The method of claim 1, wherein thetwo-dimensional non-rectangular array of rows of elements includes acenter row of elements with a first number of elements and at least onepair of rows, including a first row located on a first side of thecenter row and a second row located on an opposing side of the centerrow, wherein the first and second rows each include a second number ofelements.
 3. The method of claim 2, wherein each of the elements of thecenter row and pairs of elements of the pair of rows are in electricalcommunication with a different channel.
 4. The method of claim 2,wherein the first number of elements is greater than the second numberof elements.
 5. The method of claim 4, further comprising: focusing, viaan optical lens, a first sub-portion of the signal which is transmittedby the center row.
 6. The method of claim 4, further comprising:focusing, via a Fresnel lenses, a second sub-portion of the signal whichis transmitted by the at least one pair of rows.
 7. The method of claim4, wherein the first number of elements is the same as the second numberof elements, and wherein each element of the center row and each pair ofelements of each pair of rows, for a same column, are alternately inelectrical communication with a same respective channel.
 8. The methodof claim 7, further comprising: placing a first subset of the elementsof the center row in electrical communication with respective channels;and placing a second sub-set of the pair of elements of the pair of rowsin electrical communication with respective channels.
 9. The method ofclaim 1, further comprising: controlling a number of the transmissionseach transmit beam is based on a signal indicative of a trade-offbetween image quality and frame rate of interest of a user.
 10. Themethod of claim 1, further comprising: generating the ultrasound signalusing five-level transmitters.
 11. The method of claim 1, beamforming,comprising: determining an echo propagation delay based on a layeredmode adjusts for non-straight propagation lines.
 12. The method of claim1, beamforming, comprising: determining an echo propagation delay basedon a layered mode adjusts for non-straight propagation lines.
 13. Acomputer readable storage medium encoded with computer executableinstructions, which, when executed by a processor, cause the processorto: transmit, with a two-dimensional non-rectangular transducer array,an ultrasound signal into a field of view; receive, with thetwo-dimensional non-rectangular transducer array, echoes produced inresponse to an interaction between the ultrasound signal and structurein the field of view; and process the received echoes, therebygenerating scan lines indicative of the field of view.
 14. The computerreadable storage medium of claim 13, wherein the computer executableinstructions, which, when executed by the processor, further cause theprocessor to: control a number of the transmissions each transmit beamis based on a signal indicative of a trade-off between image quality andframe rate of interest of a user.
 15. The computer readable storagemedium of claim 13, wherein the computer executable instructions, which,when executed by the processor, further cause the processor to: generatethe ultrasound signal using five-level transmitters.
 16. The computerreadable storage medium of claim 13, wherein the computer executableinstructions, which, when executed by the processor, further cause theprocessor to: determine an echo propagation delay based on a layeredmode adjusts for non-straight propagation lines.
 17. The computerreadable storage medium of claim 13, wherein the computer executableinstructions, which, when executed by the processor, further cause theprocessor to: determine an echo propagation delay based on a layeredmode adjusts for non-straight propagation lines.
 18. The computerreadable storage medium of claim 13, wherein the two-dimensionalnon-rectangular array of rows of elements includes a center row ofelements with a first number of elements and at least one pair of rows,including a first row located on a first side of the center row and asecond row located on an opposing side of the center row, wherein thefirst and second rows each include a second number of elements.
 19. Thecomputer readable storage medium of claim 14, wherein each of theelements of the center row and pairs of elements of the pair of rows arein electrical communication with a different channel.
 20. The computerreadable storage medium of claim 14, wherein the first number ofelements is greater than the second number of elements.